Conservation of a lost national treasure

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Chapter Nine

Repair tests

Our poor sacrificial item has been torn up and punctured through, to replicate the types of damage to be repaired on The Key.

Applied puncture

Applied tear with overlapping sections

As mentioned in our last post, several repair techniques were trialled which involved mimimal use of water, to avoid causing tide lines in the areas of severe discolouration.
The first technique was a traditional one, using wheat starch paste made with water and applied to a thin hand-made Japanese tissue. The tissue was pasted out onto blotter before applying it to the item, to absorb as much water out of it as possible, but it still wasn’t dry enough, and a faint tideline did form on one end of the repair:

Starch on tissue repair, with tideline circled

Test number two used a modified cellulose adhesive (called Ethulose) dissolved in ethanol applied to the same hand-made Japanese tissue. It looked promising, but the adhesive bond proved too weak for this application:

Modified cellulose adhesive in ethanol, on Japanese tissue

The third test trialled a patch made from remoistenable Japanese tissue. The tissue had a mixture of starch paste and methyl cellulose (both made with water) applied to it, which was allowed to dry; the paper was then torn to the right size and shape for the repair. The adhesive was re-activated with a very light application of moisture from an artists’ brush. This technique worked well, providing a strong bond with an unobtrusive tissue patch, and did not cause tidelines:

Remoistenable water-based adhesive on Japanese tissue

A remoistenable repair using the ethanol-based adhesive was not trialled due to the weak nature of the adhesive evident from the second test described above.

The fourth and final test used BEVA 371 film on a very thin Japanese tissue called Tengujo. BEVA film comes in a roll on release papers, and firstly it was applied to the Tengujo using a heated spatula set to 70°C. This was then cut to shape and applied to the tear with the same heated spatula. The technique was highly successful as it provided a strong bond and an even less obvious patch than the remoistenable adhesive. The patches applied were very small but effective, which suggested they would be useful as sutures (small repair strips applied along a tear at intervals):

BEVA suture in place on tear

BEVA patch in place on puncture

After evaluating all the test results, the course of action I am choosing to take is to use small sutures of BEVA film on Tengujo tissue to hold the tears in place where the overlaps change direction:

Incorrectly overlapped tear

Correctly overlapped tear

The suturing will be done from the front, to ensure all the tears are correctly aligned, then the whole item will be turned over and each tear repaired along its entire length.